protistan

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protist、Protista、Protozoa

WordNet

1. in some classifications considered a superphylum or a subkingdom; comprises flagellates; ciliates; sporozoans; amoebas; foraminifers (同)phylum Protozoa
2. eukaryotic one-celled living organisms distinct from multicellular plants and animals: protozoa, slime molds, and eukaryotic algae (同)division Protista
3. free-living or colonial organisms with diverse nutritional and reproductive modes (同)protistan

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2012/07/15 15:54:16」(JST)

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Protist Temporal range: Neoproterozoic – Recent
Scientific classification
Domain:	Eukarya
Kingdom:	Protista* Haeckel, 1866
Typical phyla
Chromalveolata Heterokontophyta Haptophyta Cryptophyta (cryptomonads) Alveolata Dinoflagellata Apicomplexa Ciliophora (ciliates) Excavata Euglenozoa Percolozoa Metamonada Rhizaria Radiolaria Foraminifera Cercozoa Archaeplastida (in part) Rhodophyta (red algae) Glaucophyta (basal archaeplastids) Unikonta (in part) Amoebozoa Choanozoa Many others; classification varies

Protists ( /ˈproʊtɨst/) are a diverse group of eukaryotic microorganisms. Historically, protists were treated as the kingdom Protista, which includes mostly unicellular organisms that do not fit into the other kingdoms, but this group is contested in modern taxonomy. Instead, it is "better regarded as a loose grouping of 30 or 40 disparate phyla with diverse combinations of trophic modes, mechanisms of motility, cell coverings and life cycles."

The protists do not have much in common besides a relatively simple organization—either they are unicellular, or they are multicellular without specialized tissues. This simple cellular organization distinguishes the protists from other eukaryotes, such as fungi, animals and plants.

The term protista was first used by Ernst Haeckel in 1866. Protists were traditionally subdivided into several groups based on similarities to the "higher" kingdoms: the unicellular "animal-like" protozoa, the "plant-like" protophyta (mostly unicellular algae), and the "fungus-like" slime molds and water molds. These traditional subdivisions, largely based on superficial commonalities, have been replaced by classifications based on phylogenetics (evolutionary relatedness among organisms). However, the older terms are still used as informal names to describe the morphology and ecology of various protists.

Protists live in almost any environment that contains liquid water. Many protists, such as the algae, are photosynthetic and are vital primary producers in ecosystems, particularly in the ocean as part of the plankton. Other protists, such as the Kinetoplastids and Apicomplexa, are responsible for a range of serious human diseases, such as malaria and sleeping sickness.

Classification

Historical classifications

The first division of the protists from other organisms came in the 1830s, when the German biologist Georg August Goldfuss introduced the word protozoa to refer to organisms such as ciliates and corals. This group was expanded in 1845 to include all "unicellular animals", such as Foraminifera and amoebae. The formal taxonomic category Protoctista was first proposed in the early 1860s by John Hogg, who argued that the protists should include what he saw as primitive unicellular forms of both plants and animals. He defined the Protoctista as a "fourth kingdom of nature", in addition to the then-traditional kingdoms of plants, animals and minerals. The kingdom of minerals was later removed from taxonomy by Ernst Haeckel, leaving plants, animals, and the protists as a “kingdom of primitive forms”.

Herbert Copeland resurrected Hogg's label almost a century later, arguing that "Protoctista" literally meant "first established beings", Copeland complained that Haeckel's term protista included anucleated microbes such as bacteria. Copeland's use of the term protoctista did not. In contrast, Copeland's term included nucleated eukaryotes such as diatoms, green algae and fungi. This classification was the basis for Whittaker's later definition of Fungi, Animalia, Plantae and Protista as the four kingdoms of life. The kingdom Protista was later modified to separate prokaryotes into the separate kingdom of Monera, leaving the protists as a group of eukaryotic microorganisms. These five kingdoms remained the accepted classification until the development of molecular phylogenetics in the late 20th century, when it became apparent that neither protists nor monera were single groups of related organisms (they were not monophyletic groups).

Modern classifications

Currently, the term protist is used to refer to unicellular eukaryotes that either exist as independent cells, or if they occur in colonies, do not show differentiation into tissues. The term protozoa is used to refer to heterotrophic species of protists that do not form filaments. These terms are not used in current taxonomy, and are retained only as convenient ways to refer to these organisms.

The taxonomy of protists is still changing. Newer classifications attempt to present monophyletic groups based on ultrastructure, biochemistry, and genetics. Because the protists as a whole are paraphyletic, such systems often split up or abandon the kingdom, instead treating the protist groups as separate lines of eukaryotes. The recent scheme by Adl et al. (2005) is an example that does not bother with formal ranks (phylum, class, etc.) and instead lists organisms in hierarchical lists. This is intended to make the classification more stable in the long term and easier to update. Some of the main groups of protists, which may be treated as phyla, are listed in the taxobox at right. Many are thought to be monophyletic, though there is still uncertainty. For instance, the excavates are probably not monophyletic and the chromalveolates are probably only monophyletic if the haptophytes and cryptomonads are excluded.

Metabolism

Nutrition in some different types of protists is variable. In flagellates, for example, filter feeding may sometimes occur where the flagella find the prey. Other protists can engulf bacteria and digest them internally, by extending their cell membrane around the food material to form a food vacuole. This is then taken into the cell via endocytosis (usually phagocytosis; sometimes pinocytosis).

Nutritional types in protist metabolism

Nutritional type	Source of energy	Source of carbon	Examples
Phototrophs	Sunlight	Organic compounds or carbon fixation	Algae, Dinoflagellates or Euglena
Organotrophs	Organic compounds	Organic compounds	Apicomplexa, Trypanosomes or Amoebae

Reproduction

Some protists reproduce sexually (gametes), while others reproduce asexually (binary fission).

Some species, for example Plasmodium falciparum, have extremely complex life cycles that involve multiple forms of the organism, some of which reproduce sexually and others asexually. However, it is unclear how frequently sexual reproduction causes genetic exchange between different strains of Plasmodium in nature and most populations of parasitic protists may be clonal lines that rarely exchange genes with other members of their species.

Role as pathogens

Some protists are significant pathogens of both animals and plants; for example Plasmodium falciparum, which causes malaria in humans, and Phytophthora infestans, which causes late blight in potatoes. A more thorough understanding of protist biology may allow these diseases to be treated more efficiently.

Researchers from the Agricultural Research Service are taking advantage of protists as pathogens in an effort to control red imported fire ant (Solenopsis invicta) populations in Argentina. With the help of spore-producing protists such as Kneallhazia solenopsae the red fire ant populations can be reduced by 53-100%. Researchers have also found a way to infect phorid flies with the protist without harming the flies. This is important because the flies act as a vector to infect the red fire ant population with the pathogenic protist.

See also

• Protistology

References

External links

• Tree of Life: Eukaryotes
• A java applet for exploring the new higher level classification of eukaryotes
• Plankton Chronicles - Protists - Cells in the Sea - video

English Journal

• Cell proteome variability of protistan mollusc parasite Perkinsus olseni among regions of the Spanish coast.

• Fernández-Boo S1, Villalba A, Cao A.
• Diseases of aquatic organisms.Dis Aquat Organ.2015 Apr 8;113(3):245-56. doi: 10.3354/dao02835.
• We evaluated the proteome variability of in vitro-cultured Perkinsus olseni cells deriving from 4 regions of the Spanish coast: the rías of Arousa and Pontevedra (Galicia, NW Spain), Carreras River in Huelva (Andalusia, SW Spain) and Delta de l'Ebre (Catalonia, NE Spain). P. olseni in vitro clonal
• PMID 25850402

• Estimating Protistan Diversity Using High-Throughput Sequencing.

• Hu SK1, Liu Z, Lie AA, Countway PD, Kim DY, Jones AC, Gast RJ, Cary SC, Sherr EB, Sherr BF, Caron DA.
• The Journal of eukaryotic microbiology.J Eukaryot Microbiol.2015 Apr 7. doi: 10.1111/jeu.12217. [Epub ahead of print]
• Sequencing hypervariable regions from the 18S rRNA gene is commonly employed to characterize protistan biodiversity, yet there are concerns that short reads do not provide the same taxonomic resolution as full-length sequences. A total of 7,432 full-length sequences were used to perform an in silico
• PMID 25851049

• High diversity of protistan plankton communities in remote high mountain lakes in the European Alps and the Himalayan mountains.

• Kammerlander B1, Breiner HW2, Filker S2, Sommaruga R3, Sonntag B4, Stoeck T5.
• FEMS microbiology ecology.FEMS Microbiol Ecol.2015 Apr;91(4). pii: fiv010. doi: 10.1093/femsec/fiv010. Epub 2015 Jan 27.
• We analyzed the genetic diversity (V4 region of the 18S rRNA) of planktonic microbial eukaryotes in four high mountain lakes including two remote biogeographic regions (the Himalayan mountains and the European Alps) and distinct habitat types (clear and glacier-fed turbid lakes). The recorded high g
• PMID 25764458

Japanese Journal

• Eukaryotic plankton diversity in the sunlit ocean.

• Science 348(6237), 2015-05-22
• NAID 120005608038

• Molecular phylogenetic and diversity analysis of protistan microplankton based on 18S rRNA gene sequences (日本プランクトン学会2014年度春季シンポジウム 遺伝子解析とプランクトン研究)

• 日本プランクトン学会報 = Bulletin of the Plankton Society of Japan 62(1), 49-53, 2015-02
• NAID 40020411661

• Protistan grazing and viral lysis losses of bacterial carbon production in a large mesotrophic lake (Lake Biwa)

• Limnology 15(3), 257-270, 2014-08
• NAID 120005477386

Related Links

• Protistan | Define Protistan at Dictionary.com

Protistan definition, any of various one-celled organisms, classified in the kingdom Protista, that are either free-living or aggregated into simple colonies and that have diverse reproductive and nutritional modes, including the Word ...

• Protistan - definition of protistan by The Free Dictionary

Define protistan. protistan synonyms, protistan pronunciation, protistan translation, English dictionary definition of protistan. n. Any of numerous eukaryotic organisms that are not fungi, plants, or animals and are chiefly unicellular ...

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「protist」

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